The invention relates to a method of varying the comfort level of gear shifts that are performed by an automated gear-shifting transmission. A set of shift parameters controlling the comfort level of gear shifts of the transmission is modified based on detected driving parameters characterizing a current traveling situation and based on a shift program mode. The shift program mode is either selected by the driver or automatically determined within a range of available shift program modes that are associated with a value range of a characteristic parameter. In determining the shift parameters as a function of the detected driving parameters, the transmission controller uses a functional correlation that depends on the current value of the characteristic parameter. In some systems, the current value of the characteristic parameter is determined on the basis of one or more of the detected driving parameters. The invention further relates to an apparatus that is operable to perform the inventive method. Also included in the scope of the invention is a method of monitoring the proper functioning of a controller device of an automated transmission.
The known state of the art offers gear-shifting transmissions for motor vehicles in numerous configurations. The term gear-shifting transmission in the conventional sense has been understood mostly to mean a manual transmission where the driver of the vehicle shifts gears by moving a manual shift lever within the constraints or tracks of a guide pattern, e.g., an H-pattern with a neutral selector track and engagement tracks for the individual gear ratios. In addition to these manually operated transmissions, some automated gear-shifting transmissions have already become known in which the movements along the selector track and the engagement tracks of the shift pattern are performed for example by actuators that are arranged on the gear-shifting transmission and are controlled by a program.
In automated transmissions of the foregoing description, a gear change is made by first taking the clutch of the vehicle out of engagement, shifting out of the currently engaged gear, shifting into the new gear, and re-engaging the clutch.
The automated gear-changing process should conform to the wishes of the driver in regard to the times at which the gear changes occur and also in regard to the level of driving comfort. The wishes of the driver may for example be determined through an evaluation of a current position of the gas pedal, e.g., whether the driver depresses the pedal lightly, whether the engine is running below idling speed, or whether the driver commands full power from the engine. In addition, the current traveling situation of the vehicle has to be taken into account for each gear shift, for example whether the vehicle is traveling uphill, or whether the engine is giving traction or running in an engine-brake mode.
The driver will expect the gear changes to run in a manner that meets his preferences. The gear-shifting process in an automatic transmission uses characteristic curves or functions for up-shifting and down-shifting. There are sets of characteristic curves corresponding to different driver-selectable programs for the control of the automatic transmission. The characteristic curves associated with the different gear ratios form a characteristic curve field or characteristic data array.
By offering a choice of control programs, the vehicle allows the driver to have an influence on the automatic shift process. With the so-called automated gear-shifting transmission (in the sense of the term that was defined above), there is the same need to take the driver""s preferences into account in the gear shifting process. For example, the vehicle may have a sport-mode, i.e., a gear-shifting program that offers a sportier kind of shifts that take less time.
There may also be a winter mode for driving on a snow-covered road, in which case the entire gear-shifting process is performed gently, e.g., with a slow cutback of the engine torque before disengaging the clutch and an equally slow torque build-up after the shift has been completed. The vehicle may further have a manual mode where the driver can initiate a gear shift by operating a shift lever arranged inside the vehicle, or an economy mode for a fuel-saving way of driving, or a special mountain-driving mode. As these examples of shift-program modes illustrate, a vehicle can be equipped with a multitude of driving modes or shift program modes, as they are variously referred to, among which the driver may either make his own selection, or which may be automatically adopted by the transmission controller, e.g., after the on-board computer has detected the presence of mountainous road characteristics.
In addition to the aforementioned parameter that characterizes how fast the engine torque is lowered before disengaging the clutch and how fast the engine torque is restored to normal strength after the gear shift, there are a multitude of other parameters that have a significant influence on the transient phases of the power train during gear shifts and thus manifest themselves through the level of shifting comfort experienced by the driver. As a further example of such a parameter, one could mention the speed at which the clutch is disengaged before shifting out of the current gear and reengaged after the transmission has been shifted into the new gear.
The controller which directs the actuators for shifting the gears and for moving the clutch and which also controls the engine has to take a multitude of input parameters into account which are hereinafter referred to as driving parameters and include, e.g., the traveling speed of the vehicle, the engine rpm-rate, the current engine torque, and the currently engaged ratio, among others. Based on this input, the controller determines output parameters, hereinafter referred to as shift parameters, which include for example the force and speed of the shift actuation in the transmission, the speed at which the engine torque is cut back, the speed at which the clutch is disengaged and reengaged, and the speed at which the engine torque is restored after the new gear has been engaged.
The values that the controller can assign to the shift parameters are subject to certain constraints and limitations, because the power train of a vehicle represents a dynamic system that is capable of oscillating and has resonance frequencies. Thus, as an example, the shift parameter that determines the lowering and raising of the engine torque, or the parameter for the disengagement of the clutch, have certain ranges of values that must be avoided because they could cause resonances in the power train which would manifest themselves as a shaking of the vehicle, making gear shifts substantially less comfortable and possibly causing damage to the power train.
Based on the large number of possible driving programs or shift program modes and the driving parameters that have to be evaluated by the programs, such as e.g. the current gas-pedal depression and the currently engaged gear, there are a large number of characteristic curve fields or arrays that have to be optimized, so that the shift parameters as a function of the drive parameters will be determined in a manner that takes the engine characteristics as well as the driver""s preferences into account. In the design of the transmission controller, it is therefore necessary to determine vehicle-specific shift profiles for the shift parameters and store them in the form of data arrays. Because the number of characteristic curve fields for automated gear-shift transmissions can exceed 15 and can even go higher in case additional adaptations have to be made by the transmission controller, the field of characteristic shift profiles will be represented by a very large data array which has to be determined and stored and which will have to be evaluated by the transmission controller during operation of the vehicle in order to achieve gear shifts that conform to the driver""s wishes and the current traveling situation. Since the data-arrays would have to be adapted in a vehicle-specific manner, an inordinate amount of time and expense would be required to perform the adaptation.
It is therefore the object of this invention to propose a less expensive and less complicated method of modifying the shift behavior of an automated gear-shifting transmission. In addition to the method, the invention aims to provide a device to perform the method. A further objective is to propose a method of monitoring the correct functioning of a controller device of an automated gear-shifting transmission.
The invention proposes a method of setting or changing the comfort level of gear shifts that are performed by an automated gear-shifting transmission. According to the method, a shift program mode is either selected or automatically determined among a plurality of shift program modes available in a transmission control device of the motor vehicle. The different shift program modes are distinguished by different values of a characteristic parameter. At the time when a gear shift is to be performed in the transmission, the method goes through the step of detecting the values of driving parameters that are characteristic of a current driving situation of the vehicle. Based on the detected driving parameter values, a next step of the method is to determine a set of shift parameter values controlling the shift behavior of the transmission. The shift parameters are functionally dependent on the detected driving parameters. To determine the shift parameter values, the method uses the inventive concept of determining minimum and maximum values that can be assumed by the shift parameters in the current driving situation, depending on the value of the characteristic parameter. Actual shift parameter values for the impending gear shift are then calculated as intermediate values between the minimum and maximum values, whereupon the gear shift is performed with the calculated actual shift parameter values.
What motivated the invention was the recognition that the gear-changing process in an automated gear-shifting transmission is influenced by a multitude of input parameters, referred to herein as driving parameters that depend on a current driving situation of the vehicle and/or are influenced by the driver of the vehicle. Based on the driving parameters, shift parameters controlling the comfort level of the shift process would have to be made available in the form of voluminous look-up tables to be accessed by a controller device. The values in the look-up table would have to be determined specifically for each vehicle model and for each gear ratio of the automated transmission in order to achieve a gear change that will be experienced as harmonious and consistent within itself.
The driving parameters include specific factors such as: a signal indicating that the vehicle is traveling through a curve; a signal indicating a shift program mode selected by the driver; a signal indicating the amount of gas-pedal depression; a signal indicating the currently engaged gear; a signal indicating that the vehicle is traveling uphill; a signal indicating whether the driver has selected an automatic or manual shift mode; and a signal characterizing the type of driver as sport-oriented or comfort-oriented or somewhere in between. The driver""s preferred style can be determined, e.g., by monitoring the degree of pedal depression over some period of time.
The shift parameters, on the other hand, include for example: the speed at which the clutch should be taken out of engagement before a gear change so as to avoid a jolt in connection with the clutch disengagement; the rate at which the engine torque is cut back before the gear change so as to avoid a jolt from the torque decrease; the speed and force applied in actuating internal elements of the transmission during the synchronization process; the speed of moving the clutch back into engagement after the gear change; the speed of passing through the slipping phase at the gripping point of the clutch, and the rate of restoring the engine torque after the gear changing process.
The invention was motivated among other reasons by a desire to avoid the enormous effort that would have to be undertaken for each vehicle model and each gear ratio of the automated transmission to determine the tabulated arrays of shift parameter values in function of the driving parameter values. According to the invention, only the maximum and minimum values are determined and stored that the shift parameter values as functions of the driving parameter values can assume within the range of the aforementioned characteristic parameter. In subsequent actual operating situations of the vehicle, the driving parameters for a current driving situation of the vehicle are detected, and the applicable shift parameter values are calculated in real time as intermediate values between the aforementioned minimum and maximum values, rather than looking up the shift parameter values from a tabulated data array stored in a memory.
The values referred to as minimum and maximum values should be understood in a general sense as first and second values. It is not necessary for the first value to be a minimum and for the second value to be a maximum. The illustrated examples where the first value represents a minimum and the second value represents a maximum were chosen merely for the sake of clarity. As an example of a reverse correlation, if the time interval for the clutch disengagement were used instead of the speed of the clutch disengagement, the minimum speed would correlate to the maximum time interval and vice versa. For the determination of an intermediate value according to the invention, it is irrelevant which of the two end values represents the minimum and which represents the maximum.
The method further includes that each of the shift program modes that can be selected by the driver or determined by the transmission controller is associated with a characteristic parameter value. Based on the endpoints of the value range for the characteristic parameter, there is a maximum and a minimum for the values that a shift parameter can assume. In an actual shift situation, the transmission controller finds the maxima and minima of the shift parameter values based on the detected driving parameter. The actual shift parameters are then calculated as intermediate values depending on where the characteristic parameter value falls between the end points of the value range. The actual shift parameters are used to perform the shift process.
Thus, according to the invention, the data that have to be stored in memory as look-up tables consist only of the maximum and minimum boundary curves of the shift parameter fields corresponding to the endpoints of the characteristic parameter value range. In an actual driving situation, the applicable driving parameter values are determined as intermediate values between the maximum and minimum boundary curves. This eliminates the need to determine a multitude of characteristic fields and tabulate the data for each curve of each field as a look-up array for the transmission controller.
The invention proposes a further method of setting or changing the comfort level of gear shifts that are performed by an automated gear-shifting transmission using a shift program mode that is either selected or automatically determined among a plurality of shift program modes available in a transmission control device of the motor vehicle. At the time when a gear shift is to be performed in the transmission, the method goes through the step of detecting one or more driving parameter values that are characteristic of a current driving situation of the vehicle. A next step of the method is to determine a characteristic parameter value that is dependent on the detected driving parameter values. Minimum and maximum curves of shift values in function of driving values are stored for look-up based on the characteristic parameter value. The shift process is performed with shift values that are determined as intermediate values between the minimum and maximum shift parameter values at the abovementioned characteristic parameter value.
In accordance with the further method just described, a first step consists of detecting the current driving parameters and determining a current characteristic parameter value dependent on the detected driving parameters.
Dependent on the characteristic parameter value, minimum and maximum values are determined that can be assumed by the shift parameters in function of the driving parameters. Dependent on the current characteristic parameter value, intermediate values of the shift parameters are determined as intermediate values between the minimum and maximum values, and the shift process is performed with the shift parameters that are based on the current value of the characteristic parameter.
Under this embodiment of the inventive method, it is likewise unnecessary to store complete tabulated arrays of shift parameter fields in a memory of the transmission controller in order to cover every possible combination of driving parameters and driver preferences in order to perform all shift maneuvers in a manner that is appropriate for the driving situation. According to the invention, the data that have to be stored in memory for each characteristic parameter value as look-up tables consist only of the maximum and minimum boundary curves of the shift parameter fields in function of the driving parameters. In an actual driving situation, the applicable shift parameter values are determined as intermediate values dependent on the currently effective driving parameter values. The shift process is performed with the applicable shift parameter values in a manner that conforms to the driver""s inputs as well as the actual driving situation.
In accordance with a further developed embodiment of either of the foregoing methods, the intermediate values are calculated by interpolation between the minimum and maximum values. The interpolation can be a conventional linear interpolation, but the scope of possibilities also includes non-linear forms of interpolation. It is also conceivable that for driving situations that occur infrequently, i.e., driving parameter values that are found only in rare cases, the current shift parameter values may be determined by an extrapolation going outside the interval between the previously determined minimum and maximum values.
In accordance with a further embodiment of the method, shift parameter values that would cause an oscillatory shaking of the vehicle during a gear-changing process are excluded from use in a gear shift.
The concept of excluding certain values or value ranges of shift parameters recognizes the fact that the power train of a vehicle is a dynamic system that is capable of oscillating at certain resonance frequencies and that the resonances can be excited by certain ways of performing a gear shift. Consequently, it is possible for a gear-shifting process to cause shaking oscillations of the vehicle which would be felt by the driver as uncomfortable or disharmonious. In addition, such shaking vibrations also involve the risk of damage to the power train. Therefore, when determining shift parameters in response to a current driving situation or to a driver command, the inventive method provides the concept of excluding shift parameter values that would cause an oscillatory shaking of the vehicle.
In accordance with a further concept of the invention, the shift parameters for initiating the gear shift process and the shift parameters for ending the gear shift process are determined in connection with each other in order to achieve a shift process that is consistent within itself.
This concept of the invention takes into account that the respective shift parameters for the beginning phase and the ending phase of a shift process, for example the respective rates of cutting back the engine torque before the gear change and restoring it again after the gear change, have to be matched to each other in order to achieve a shift that is consistent within itself. A self-consistent shift process is experienced by the driver as harmonious or well-matched. This is the case, for example, if the respective rates of cutting back and restoring the engine torque are in a ratio of about two to one, i.e., if the time interval for restoring the engine torque is about twice as long as the time interval for cutting back the engine torque.
In contrast, if the ratio between the aforementioned rates is significantly different from a ratio of two to one, e.g., if a very fast cutback were combined with a very slow restoration of the engine torque, the driver would find the fast cutback rate to correspond to a lively, sporty style of driving, while the slow torque restoration, in comparison, would give a sluggish impression, so that the gear shift would not be consistent within itself.
In addition to the rates of cutting back and restoring the engine torque, other shift parameters that strongly influence the transient properties of the shift process include in particular the speed and force applied to actuating the gear change in the transmission.
According to the invention, the detection of driving parameters includes parameters that depend on a current input from the driver as well as parameters that depend on a current traveling situation of the vehicle. Thus, the process of determining the shift parameters takes the driver""s wishes as well as the actual traveling situation into account. In other words, the inventive method uses a driver-input detection and a traveling-situation detection as a basis for determining the shift parameters.
Shift parameters that are subject to change from one shift process to the next in response to varying driving parameters include in particular the speed at which the engine torque is cut back before the gear change, the speed at which the clutch is taken out of engagement, the speed and force applied by the actuators to change gears in the transmission, the speed of re-engaging the clutch, and the speed of building up the engine torque again after the gear change.
The scope of the invention also includes an apparatus for performing the method described above. This apparatus consists of or includes a processor unit that evaluates the driving parameters as well as the parameters of the shift program mode or shift mode that has been selected by the driver or automatically determined. The processor unit further looks up shift parameter values as well as a characteristic parameter value of the currently effective shift program mode in a memory device, or it calculates the characteristic parameter value on the basis of the driving parameters. Based on the detected driving parameters, the looked-up shift parameter values and the characteristic parameter, the device computes the actual shift parameters for performing the impending gear shift.
In other words, the processor unit evaluates the detected current driving parameter values and also detects or determines the driving program or shift program mode that is to be used for performing the impending gear shift of the automated transmission. The processor unit further has the capability to look up shift parameter values that are stored in a memory device as functions of driving parameter values in the form of look-up tables for the maximum and minimum shift parameter values associated with each driving parameter value. In addition, the device looks up a characteristic parameter that identifies the driving program or shift program mode and whose values for the different possible shift program modes are likewise stored in the memory device. Alternatively or in addition, the processor unit could have the capability to calculate the characteristic parameter value from current driving parameters. Based on the detected current driving parameters and the currently applicable characteristic parameter, the processor unit determines the shift parameter values that are to be used in the current gear-shifting process. The driving parameters or input parameters may also include a driver input, for example in the form of a signal that indicates the current degree of gas-pedal depression.
Based on the calculated shift parameters, the processor unit directs the shift process through some or all of the different phases, such as disengaging the clutch, shifting out of the currently engaged gear, shifting into the new gear, re-engaging the clutch, where the processor unit controls the time length of the respective phase and/or the force, torque or speed of the respective actuators, or other factors.
According to a further developed version of the invention, the apparatus also includes a device for detecting and/or evaluating error situations. The device has error counters whose count is incremented or decremented depending on the detected driving parameters. After a predetermined error count has been exceeded, a diagnostic message is given out and/or the re-engagement of the clutch is postponed until the error count has been reset in response to the driving parameters.
In short, the inventive apparatus is also configured with the capability to detect and evaluate error situations. To perform this function, the apparatus may be equipped with an error counter that is incremented dependent on the detected driving parameters, i.e., the count can be increased as well as decreased in response to the driving situation.
The limit or threshold for the error count that triggers an action, such as sending a diagnostic message or putting a hold on a clutch re-engagement until the error count has been reset, can likewise take on different values dependent on the detected driving parameter values. A reset of the error count is possible, e.g., in response to current driving parameter values indicating that the vehicle is standing still and that no gear is engaged. To provide the system with a redundant degree of safety, it is also possible to design the apparatus with two processor units of the foregoing description, where the processor units would have the capability to monitor each other.
The invention further includes a method of monitoring the correct functioning of the controller device of an automated gear-shifting transmission. The controller device has at least one error counter that can count up and/or down. The monitoring method includes the steps of incrementing the count at the occurrence of an error situation and decrementing the count when no error is detected, and initiating an action when the error count reaches a threshold value, wherein the increment and/or decrement is variable.
With the concept of varying the increment or decrement based on the driving situation of the vehicle with the automated transmission, the time interval for reaching the trigger limit and a subsequent action can be varied. For example, the action may be to reset the transmission controller when the trigger limit is reached. This procedure has the advantage that the restart of the controller prevents the control program from getting stuck in a faulty action or routine, because a faulty action is terminated and the controller returns on its own to a sound operating mode.
The error count threshold can also be varied depending on the driving situation of the vehicle. the trigger threshold may for example be raised when the vehicle is moving and lowered when the vehicle is standing still.
The action that is triggered by reaching the threshold can be variable dependent on the driving situation of the vehicle.
As an example of this concept, to avoid a potentially critical situation while the vehicle is standing still with a gear engaged, a movement of the clutch actuator to engage the clutch is stopped if the error-count limit has been reached, and the clutch engagement is released only after the error count has been decremented or the counter has been reset. It can be advantageous if the error count limit is lowered when the vehicle is standing still with a gear engaged, so that the trigger limit is reached sooner than when the vehicle is moving, because a critical situation such as the vehicle taking off on its own cannot occur while the vehicle is being driven by a driver, so that it is permissible to delay the point at which the error count limit would cause an action of the controller device.
Finally, the scope of the invention also includes the concept of providing two processors in the controller device, wherein at least one of the processors has an error counter and the processors mutually monitor each other.